you want to fit bmw wheels on a s13? should be do-able , but you'd need a special wheel stud/lug setup on one of the 5 studs to get around the 4/5 stud issue..... Might be expensive. 5 stud to 5stud is much easier.
If you're happy having spacers then you don't need low offsets. Just get massive 4x114.3 spacers and fit cheap easy-to-find high offset wheels.
5x114.3 to 5x120 would be easy, but it's impossible to make simple 4x114.3 to 5x120 adapters because allways one hole would be on other. There are only two options: 1. Make those adapters, but leave wheel only with 4 bolts. 2. Make two piece adapters. You attach one piece to a hub, ten second piece to first piece, then wheel to a second piece. In that case adapters will be thick, also you'll have 14 bolts on each wheel. For 4x114.3 to 5x114.3 will be easyier, then one hole will be shared. You'll need to install long stud in your hub for that hole.